Water flow pressure in your house can depend on many factors: dirt accumulation on the walls of pipes, defect of mixers, water usage by a lot of people simultaneously in one house and etc. Water pressure on the first floors of multistorey houses always higher than on the last floors.
Low pressure affects negatively on an engineering system in a house. However high pressure is more dangerous because it can cause a damage of sanitary ware, pipes and flexible hoses. There is a defined pressure rate at which sanitary ware will operate faultlessly for many years. A minimal water pressure is 0,5 bars, a maximal one is 9 bars. An optimum range is from 1 to 5 bars. If pressure of the pipes is in excess of 5 bars, all sanitary ware is exposed to hydraulic shocks. In such situation mixer, flexible hose or ball valve can be damaged. As a result your flat will be flooded. Another widespread problem is when water flow pressure in the pipes for hot and cold water has the difference more than for 1 bar. This problem can cause emergency situations and breakage of sanitary ware. Note that it will not be a guarantee case.
To avoid such problems it is necessary to install a pressure reducing valve. It adjusts the outlet pressure and prevents your sanitary ware from hydraulic shocks. Especially it is needed in flats located on the first three floors of multistorey houses.